The invention relates to a diode laser array and to a method for manufacturing a laser diode array.
High-power diode lasers today are based primarily on broad-area lasers with chip dimensions of 0.5 . . . 1 mm×1 . . . 4 mm and a chip height of 100 . . . 150 μm. The laser active layer of the chip, in which the laser radiation or light is generated, is aligned along the larger edge length of the chip; the cleaved edges having very good flatness and therefore forming the end and output mirrors of the laser. The laser radiation exits the output mirror at a width of typically only 50 . . . 200 μm from the chip material. An emitter width of 100 μm can achieve an output power of up to 15 W.
For high-power diode layers, such wide area lasers or emitters are combined to form laser bars, in which up to one hundred individual emitters are provided successively on a length of up to 10 mm. The end mirror and output mirror then both extend over the entire length of such a laser bar, in order to achieve an output power between 100 and 150 W, for example.
For cooling, the laser bars are normally soldered with their p-side to heat sinks, in particular to active heat sinks, i.e. to heat sinks which, or the canals or canal structures of which, are flowed through with a coolant, for example cooling water.
In particular in the existing art, in order to increase the power output, diode laser arrays are stacked, namely with several laser bars arranged one on top of the other and each provided on a heat sink, respectively.
The disadvantage of such diode laser arrays or arrangements known in the art is that the laser bars or emitters are cooled on only one side, i.e. on the mounting side or p-side, while the other side, for example the n-side of the laser chips of the laser bar is used only for bonding.
Further, especially the stacked diode layer arrays or arrangements known in the art have a complex design and are susceptible to failure, in particular because the design provides for numerous transition points for the cooling water, which have to be sealed, for example with O-rings. Further, numerous transition points or connections are also necessary for the power supply.
Known in the art is the DCB or Direct Copper Bonding technology, which is used to bond metal layers or sheets (e.g. copper sheets or foils) with each other and/or with ceramic or ceramic layers, namely using metal or copper sheets or metal or copper foils, which are provided on their surfaces with a layer or coating (hot-melt layer) resulting from a chemical bond between the metal and a reactive gas, preferably oxygen. In this method, which is described for example in US-PS 37 44 120 and in DE-PS 23 19 854, this layer or coating (hot-melt layer) forms a eutectic with a melting temperature below the melting temperature of the metal (e.g. copper), so that the layers can be bonded to each other by placing the foil on the ceramic and heating all layers, namely by melting the metal or copper essentially only in the area of the hot-melt layer or oxide layer.
This DCB process then comprises, for example, the following process steps:                oxidation of a copper foil so as to produce an even copper oxide layer;        a placing the copper foil on the ceramic layer;        heating the composite to a process temperature between approx. 1025 and 1083° C., e.g. to approx. 1071° C.;        cooling to room temperature.        
Also known in the art is the so-called active soldering method (DE 22 13 115; EP-A-153 618), e.g. for bonding metal layers or metal foils forming metallizations, in particular also of copper layers or copper foils, with ceramic material. In this process, which is used especially for manufacturing a metal-ceramic substrate, a bond is produced at a temperature of ca. 800-1000° C. between a metal foil, for example copper foil, and a ceramic substrate, for example aluminum nitride ceramic, using a hard solder, which in addition to a main component such as copper, silver and/or gold also contains an active metal. This active metal, which is at least one element of the group Hf, Ti, Zr, Nb, Ce, creates a bond between the solder and the ceramic through a chemical reaction, while the bond between the solder and the metal is a metallic hard solder bond.
It is an object of the invention is to present a diode laser array that eliminates the disadvantages of the prior art and enables a simplified design with an improved cooling effect.